High solids ethylene-vinyl acetate latex

ABSTRACT

The present invention is directed to an ethylene-vinyl acetate dispersion and a process for making the dispersion by polymerizing a monomer mixture having vinyl acetate and ethylene in a batch process, in the presence of a stabilizing system of polyvinyl alcohol and without added surfactants, to form an ethylene-vinyl acetate polymer dispersion. The copolymer dispersion has a solids level of greater than 65 percent by weight, and a viscosity of less than 5000 mPa.s when measured at 65 percent solids at 25° C. The dispersion can be dried to form a redispersible powder. Both the dispersion and powder are useful in adhesive and coating formulations.

FIELD OF THE INVENTION

[0001] This invention relates to a high solids ethylene-vinyl acetatedispersion and a process for producing such a dispersion by batchpolymerization of a monomer mixture having vinyl acetate and ethylene,in the presence of a stabilizing system of polyvinyl alcohol withoutadditional surfactants. The dispersion has a solids level of greaterthan 65 percent by weight, and a viscosity of less than 5000 mPa.s whenmeasured at 65 percent solids at 25° C. The dispersion can be dried toform a redispersible powder. Both the dispersion and powder are usefulin adhesive, coating and cementitious formulations.

BACKGROUND OF THE INVENTION

[0002] Ethylene-vinyl acetate dispersions, and powders produced bydrying these dispersions, are widely used in adhesive, coating andcementitious formulations. High solids dispersions are of specialinterest due to favorable economics through increasing the reactorefficiency. High solid dispersions that will be spray dried benefit fromhaving less water to remove, increasing the efficiency of the spraydryer in both throughput and energy savings. A high solids dispersionmust have a low enough viscosity for practical use.

[0003] U.S. Pat. Nos. 4,921,898; 5,070,134; 5,629,370; 5,936.020;5,939,505; and 6,001,916 all disclose ethylene-vinyl acetate dispersionshaving a solids level of greater than 65 percent. These dispersions areproduced in a batch reactor, and using a stabilizer system of polyvinylalcohol and a surfactant. The presence of a surfactant in the dispersionnegatively affects water-resistance, spraydrying, and redispersibilityof polymer powders.

[0004] EP 1067147 discloses a continuous process for the production of ahigh solids ethylene-vinyl acetate dispersion using low molecular weightpolyvinyl alcohol as the emulsifying agent without the use of asurfactant, producing an dispersion having greater than 65 percentsolids and a viscosity of 1000 to 3000 cps at 25° C. The applicationcites that conventional batch processes have not been adapted to makehigh solids vinyl acetate/ethylene dispersions without a surfactant.

[0005] Surprisingly it has been found that an ethylene-vinyl acetatedispersion having a solids level of greater than 65 percent by weight,and a viscosity at 65 percent by weight solids of less than 5000 mPa.s.,can be produced in a batch process using polyvinyl alcohol as thestabilizer, without additional surfactants.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a polymer compositioncomprising an ethylene-vinyl acetate polymer dispersion stabilized withpolyvinyl alcohol, wherein said dispersion has a solids level of greaterthan 65 percent by weight, and wherein said dispersion has a bimodalparticle size distribution.

[0007] The invention is also directed to a process for forming anethylene-vinyl acetate polymer dispersion comprising polymerizing amonomer mixture comprising vinyl acetate and ethylene in a batchprocess, in the presence of a stabilizing system consisting of polyvinylalcohol, to form an ethylene-vinyl acetate polymer dispersion, whereinsaid copolymer dispersion has a solids level of greater than 65 percentby weight, and a viscosity of less than 5000 mPa.s when measured at 65percent solids at 25° C.

[0008] The invention is further directed to process for producing aredispersible polymer powder comprising polymerizing a monomer mixturecomprising vinyl acetate and ethylene in a batch process, in thepresence of a stabilizing system consisting of polyvinyl alcohol, toform an ethylenevinyl acetate polymer dispersion; and drying saidpolymer dispersion to form a redispersible polymer powder, wherein saidcopolymer dispersion has a solids level of greater than 65 percent byweight, and a viscosity of less than 5000 mPa.s.

[0009] The invention is also directed to the use of the high solidsdispersion and redispersible powder in adhesives, coatings andcementitious formulations.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The dispersion polymer of the present invention is formed in abatch free radical polymerization of vinyl acetate, ethylene, andoptionally other comonomers including functional monomers, in thepresence of a polyvinyl alcohol stabilizing system. Water forms thecontinuous phase, with polymer particles forming the dispersed phase.

[0011] Vinyl acetate and ethylene monomers are polymerized to form thedispersion polymer. In general, the final polymer contains from 75 to 99percent by weight of vinyl acetate, and from 1 to 25 percent by weightof ethylene. Preferably the level of vinyl acetate is from 85 to 95percent by weight and the level of ethylene incorporated is from 5 to 15percent by weight.

[0012] In addition to vinyl acetate and ethylene, one or more otherethylenically unsaturated monomers may also be present in the monomermixture at up to 15 percent by weight, preferably from 5 to 10 percentby weight of the total polymer solids. Examples of said comonomersinclude, but are not limited to, comonomers conventionally used incompositions with ethylene and vinyl esters such as acrylates andmaleates, e.g. butyl acrylate, and 2-ethylhexyl acrylate. Functionalmonomers may also be included at up to 10 percent by weight, andpreferably from 1 to 5 percent by weight. Examples of suitablefunctional monomers are carboxylic acids, such as acrylic, methacrylicand maleic acid as well as hydroxyl and amide functional monomers, e.g.hydroxyethylacrylate, hydroxypropylacrylate, acrylamide, N-vinylformamide, N-vinyl acetamide and the like. Crosslinking monomers canalso be present, such as N-methylol acrylamide, and the nalkyl estersthereof.

[0013] Additionally, certain copolymerizable monomers that assist in thestability of the copolymer dispersion, e.g., vinyl sulfonic acid and2-acrylamido-2-methylpropane sulfonic acid or their salts may be usedherein as latex stabilizers. If present, these stabilizers are added inamounts of from about 0.2 to 1 percent by weight of the monomer mixture.

[0014] The initiator is any free radical initiator, or initiator systemknown in the art. Suitable as polymerization initiators are thewater-soluble free-radical-formers generally used in emulsionpolymerization, such as hydrogen peroxide, sodium persulfate, potassiumpersulfate and ammonium persulfate, as well as t-butyl hydroperoxide, inamounts of between 0.01 and 3 percent by weight, preferably 0.1 and 1percent by weight based on the total amount of the polymer dispersion.They can be used alone or together with reducing agents such as sodiumformaldehyde-sulfoxylate, iron-II-salts, sodium dithionite, sodiumhydrogen sulfite, sodium sulfite, sodium thiosulfate, ascorbic acid,erythorbic acid as redox catalysts in amounts of 0.01 to 3 percent byweight, preferably 0.1 to 1 percent by weight, based on the total amountof the polymer dispersion. The free-radical-formers can be charged inthe aqueous emulsifier solution or be added during the polymerization indoses. Oil soluble initiators such as t-butyl hydrogen peroxide arepreferred.

[0015] The stabilizing system of the present invention is low molecularweight polyvinyl alcohol. The polyvinyl alcohol is preferably partiallyhydrolyzed polyvinyl acetate and is used in amounts of 1 to 15 percentby weight, preferably 4 to 10 percent by weight, based on the weight ofthe polymer solids. Generally, the degree of hydrolysis will vary from50 to 99 percent, preferably from 80 to 99 percent of the acetategroups. The polyvinyl alcohol should also exhibit a viscosity of about 2to 45 mPa.s., preferably 3 to 30 mPa.s, and most preferably 3 to 10mPa.s for a 4 weight percent aqueous solution at 20° C as determined bythe Hoeppler falling ball method. Exemplary of the polyvinyl alcoholcomponent include AIRVOL A205, a low molecular weight, 87 to 89 percenthydrolyzed polyvinyl acetate; and AIRVOL A203, a low molecular weight,87 to 89 percent hydrolyzed polyvinyl acetate, which are marketed by AirProducts Corporation. Blends of various polyvinyl alcohols may also beused in order to increase the water resistance of the resultant powderand can include 92 to 99 percent hydrolyzed polyvinylalcohol, such asAIRVOL A103 from Air Products or RS 105 from Kuraray.

[0016] The stabilizing system of the present invention could optionallyinclude protective colloids in addition to the polyvinyl alcohol.Examples of useful colloids include, but are not limited to,polyethylene glycol, cellulosics, and polyvinyl pyrrolidone. Thestabilizing system is free of surfactants.

[0017] The polymerization process is a batch process, involving a singlereactor with all monomer added prior to commencing the reaction. Ingeneral, the process includes charging the reactor initially with vinylacetate, ethylene, water, polyvinyl alcohol and any other suitablecomponents. This initial charge represents 100 percent of the totalmonomer charge. The ingredients may be added in any order withoutaffecting the resultant dispersion. The reactor is then heated to from40 to 60 °C., preferably about 50° C. The reactor is agitated by anysuitable means to facilitate dissolution of the ethylene. A portion ofthe initiator is added to the initial charge, with the remainder addedgradually during the reaction to maintain the reaction. Generally thereaction will last several hours, preferably up to 10 hours and mostpreferably from 1 to 4 hours.

[0018] The polymerization is carried out at a pH of between 2 and 7,preferably between 3 and 5. In order to maintain the pH range, it may beuseful to work in the presence of customary buffer systems, for example,in the presence of alkali metal acetates, alkali metal carbonates,alkali metal phosphates. Polymerization regulators, including mercaptanssuch as mercaptoacetic acid and mercaptoethanol; aldehydes; chloroform;methylene chloride and trichloroethylene, may also be added.

[0019] It has been found that a seeded process is beneficial, but notessential. A seeded process involves the addition of from 0.01 to 10percent by weight of a seed polymer, based on the weight of the finaldispersion, to the reactor charge. Preferably the seed is an ethylenevinyl acetate latex polymer stabilized with polyvinyl alcohol, as knownin the art. Most preferably the seed has a fine unimodal particle sizedistribution. An example of such a polymer is VINAMUL V3265, by NationalStarch and Chemical.

[0020] The reaction is generally continued until the residual monomercontent is below about 1 percent The reaction product is cooled slightlyand further initiator is added in order to reduce the residual monomerbelow 1000 ppm. The completed reaction product is then allowed to coolto about room temperature, while sealed from the atmosphere. Afterdegassing, the pH may then be suitably adjusted to ensure maximumstability. Other adjustments or additions may optionally be made at thistime, as desired.

[0021] The dispersion produced has a high solids level, without the needfor an additional concentration step. By high solids, as used herein, ismeant that the polymer particles are present in the dispersion at alevel of 65 percent by weight or greater, preferably 67 percent byweight or greater, and most preferably greater than 68 percent, based onthe dispersion.

[0022] The high solids dispersion of the present invention has aviscosity of a level to facilitate transport and also useful in a spraydryer, without further dilution. Preferably the viscosity of thehighsolids dispersion is less than 5,000 mPa.s., and most preferablyless than 3,000 mPas, when measured at 65 percent solids at 25° C.

[0023] Dispersions formed from the present invention have a bimodalparticle size distribution. While not being bound by any theory, it isbelieved that the bimodal distribution may be due to the formation ofboth emulsion and suspension polymers with the reaction system. Particlesizes of the dispersion particles from the process are illustrated inFIG. 1, and consist of a peak with a maximum between 0.2 and 0.5microns, and a peak with a maximum between 3 and 6 microns.

[0024] The dispersion formed in the present invention may be used in theaqueous form, or may be dried to form a redispersible powder. Drying isdone by any means known in the art, such as freeze drying, drum drying,fluidized bed, or spray drying. A preferred method is by spray dryingunder conditions known in the art.. These conditions are illustrated inthe Examples. The high solids level of the dispersions is advantageousin the drying procedure, since less water must be removed, requiringless time and expense.

[0025] Since the dispersions of the present invention are stabilizedwithout the use of surfactants, water-resistance properties are notadversely affected. This makes these dispersions, or powders formed fromthe dispersions with excellent water resistant properties. The absenceof a surfactant also improves both the spray-drying, and theredispersibility of the powder.

[0026] Typical applications for the dispersion include, but are notlimited to, to self-leveling floor screeds, ceramic tile adhesives,packaging and converting adhesive applications, and coatings. Typicalapplications for the powder include, but are not limited to adhesives,cement additives, and cementitious, gypsum based, gypsum-free, andcement-free mortars. These mortars may contain ingredients, such as forexample: quartz sand, calcium and magnesium carbonates, silicates,cellulose, calcium oxide, other minerals, or mixtures thereof

[0027] The following examples are presented to further illustrate andexplain the present invention and should not be taken as limiting in anyregard.

EXAMPLE 1

[0028] An aqueous solution was prepared by the addition of 378 g AIRVOL203 (Air Products) to 1260 g of cold demonized water whilst stirring.The mixture was heated at 85° C. for 1 hour. Once cool, 1 g of sodiumbicarbonate, 2 g of formosul (sodium formaldehyde sulphoxylate), 21 g of1% aqueous solution of ferrous sulphate, 21 g of 1% aqueous solution ofversene (ETDA complexing agent) and 341 g of 25-1808, National Starchand Chemical Company, an ethylene vinyl acetate seed latex (55% solids,12/88 ethylene/vinyl acetate stabilized with 5 parts polyvinyl alcohol)was added. The solution was stirred and the pH adjusted to 3.9-4.1 withphosphoric acid. It was then charged to a 12 litre stainless steelreaction vessel and the inlet port flushed with 200 g of deionisedwater.

[0029] The reaction vessel was purged by pressurizing to 7 bar withnitrogen twice and once with ethylene. The vessel was vented betweeneach purge.

[0030] The reaction vessel was then evacuated and 5764 g of vinylacetate was charged, followed by 630 g of ethylene. Agitation commencedat 450 rpm and the mixture was pre-emulsified for 10 minutes before thetemperature was increased to 50° C. When the temperature was constant at50° C., continuous additions of a solution of 20 g of tertiary butylhydroperoxide in 600 g of deionised water, and a solution of 10 g offormosul and 1.6 of sodium bicarbonate in 600 g of deionised water werecommenced to last 3.5 hours.

[0031] After a 2° C. exotherm the external temperature was increased to60° C. The batch temperature was allowed to increase to above 85° C. notexceeding 110° C. After the initial exotherm the reaction temperaturewas maintained at 85° C.

[0032] Once the continuous additions were complete the batch was cooledto 60° C. and a solution of 10 g of tertiary butyl hydroperoxide in 60 gof deionised water was added over 10 minutes. The reaction was held for10 minutes before a solution of 9 g of formsul in 60 g of deionisedwater was added over 10 minutes.

[0033] The reactor was cooled and the contents discharged to ade-gassing vessel containing a solution of 2 g Bevaloid 681 in 20 g ofdeionised water. The vessel was left overnight to degas then theresultant dispersion was filtered through a 120 mesh.

[0034] The resultant polymer had a solids content of 68.59%, viscosityof 2280 mPa.s, and a glass transition temperature of 17.9° C. Theethylene content by IR was recorded as 10%. The particle sizedistribution as measured using a Coulter LS230 is shown in FIG. 1 below.

EXAMPLE 2

[0035] This example was prepared using the same method as described inExample 1, but the distribution of water was modified. The initialreactor charge had 1860 g of deionized water, while the initiatorsolutions contained 353 g of deionized water each. The resultant polymerhad a solids content of 68.25%, a viscosity of 2550 mPa.s, and a glasstransition temperature of 16.3° C.

EXAMPLE 3

[0036] Example 3 was synthesized as described in Example 1, but no seedlatex was introduced into the water phase. The resultant polymer had asolids content of 68.84%, a viscosity of 3450 mPa.s, and a Tg of 11.2°C.

EXAMPLE 4

[0037] This sample was prepared in the same way as Example 1, thedifference in this case was that ferric chloride was used to catalyzethe redox reaction rather than the ferrous sulphate/versene pair. Theresultant polymer had a solids content of 68.09%, a viscosity of 2790mPa.s.s, and a Tg of 12.9° C.

EXAMPLE 5

[0038] This examples was synthesized as outlined in Example 1, thedifference was the seed latex introduced into the water phase. VINAMUL3265 (National Starch & Chemical) is an EVA (17/83) stabilized with 5parts of PVOH. The resultant polymer had a solids content of 67.3%, aviscosity of 3690 mPa.s, and a Tg of 14.4° C.

EXAMPLE 6

[0039] This example was made using the process outlined in Example 1,except that 8% AIRVOL 203 based on monomer weight was used forstabilization. The resultant polymer had a solids content of 65.22%, aviscosity of 2270 mPa.s, and a Tg of 13.13° C.

EXAMPLE 7

[0040] This example was made using the process outlined in Example 2,except that 10% AIRVOL 203 based on monomer weight was used forstabilization. The resultant polymer had a solids content of 65.0%, aviscosity of 3200 mpa.s, and a Tg of 16.76° C.

EXAMPLE 8

[0041] This example was prepared in the same way as Example 6, usingAIRVOL 502 instead of AIRVOL 203. The resultant polymer had a solidscontent of 68.35%, a viscosity of 2990 mPA.s, and a Tg of 16.3° C.

EXAMPLE 9

[0042] This example was prepared in the same way as Example 8, with 2%AIRVOL A102 and 6% AIRVOL 203 based on monomer weight used forstabilization. The resultant polymer had a solids content of 67.97%, aviscosity of 6600 mPa.s, but diluted to a viscosity of 3730 mpa.s at65.5% solids, and a Tg of 13.13° C.

EXAMPLE 10

[0043] This example was prepared using the process outlined in Example8, with 6% AIRVOL 502 and 2% GOHSENOL AL06 based on monomer weight usedfor stabilization. The resultant polymer had a solids content of 67.31%,a viscosity of 5420 mPa.s, which diluted to a viscosity of 4500 mPa.s at66.75% solids, and a Tg of 13.13° C.

EXAMPLE 11

[0044] Example 11 was prepared using the same method as Example 2, with315 g VeoVa 10 (Shell Chemicals) substituted for 315 g of vinyl acetate.The resultant polymer had a solids content of 68.1%, a viscosity of 4160mPa.s, and a Tg of 14.8° C.

EXAMPLE 12

[0045] Example 12 was prepared using the same method as Example 2, with630 g VeoVa 10 substituted for 630 g of vinyl acetate. The resultantpolymer had a solids content of 67.74%, a viscosity of 6000 mPa.s. Thisdiluted to a viscosity of 3520 mPa.s at 66.86% solids content. The Tgwas 7.6° C.

EXAMPLE 13

[0046] Example 13 was prepared using the same method as Example 2, with315 g 2-EHA substituted for 315 g of vinyl acetate. The resultantpolymer had a solids content of 67.1%, a viscosity of 1850 mpa.s, and aTg of 8° C.

EXAMPLE 14

[0047] Example 14 was prepared using the same method as Example 1, butthe stirrer speed was increased to 580 rpm. The resultant polymer had asolids content of 68.26%, a viscosity of 3900 mPa.s, and a Tg of 16.0°C.

EXAMPLE 15

[0048] Example 15 was prepared using the same ingredients as Example 1,however the order of addition was modified so the vinyl acetate wasadded at room temperature, agitation was commenced and the water phasewas added. After the water phase was loaded, the temperature was raisedprior to adding the initiators. The resultant polymer had a solidscontent of 67.64%, a viscosity of 3110 mPa.s, and a Tg of 16.3° C.

EXAMPLE 16

[0049] The dispersion from Example 14 was spray dried in the typicalmanner yielding a free flowing redispersible powder. The powder wascompared with a standard EVA redispersible powder in floor screeds andceramic tile adhesives and comparable properties were obtained regardingspread, surface hardness, mortar workability, and pot life.

[0050] These results indicate that dispersions made according to theinvention can be spray dried and redispersed in a manner similar tocurrent system, but with less energy due to the lower amount of water tobe evaporated.

What is claimed is:
 1. A polymer composition comprising anethylene-vinyl acetate polymer dispersion stabilized with polyvinylalcohol, wherein said dispersion has a solids level of greater than 65percent by weight, and wherein said dispersion has a bimodal particlesize distribution.
 2. The polymer composition of claim 1 wherein saidpolymer dispersion is surfactant free.
 3. A process for forming anethylene-vinyl acetate polymer dispersion comprising polymerizing amonomer mixture comprising vinyl acetate and ethylene in a batchprocess, in the presence of a stabilizing system consisting of polyvinylalcohol, to form an ethylene-vinyl acetate polymer dispersion, whereinsaid copolymer dispersion has a solids level of greater than 65 percentby weight, and a viscosity of less than 5000 mPa.s when measured at 65percent solids at 25° C..
 4. The process of claim 3 wherein saidethylene-vinyl acetate polymer dispersion comprises from 75 to 99percent by weight vinyl acetate units and from 1 to 25 percent by weightof ethylene units, based on polymer solids.
 5. The process of claim 3wherein said polyvinyl alcohol is present at from 1 to 15 percent, basedon the weight of the polymer solids.
 6. The process of claim 5 whereinsaid polyvinyl alcohol is present at from 4 to 10 percent, based on theweight of the polymer solids.
 7. The process of claim 3 wherein saidpolymer dispersion has a bimodal particle size distribution.
 8. Theprocess of claim 3 wherein said polymer dispersion is surfactant free.9. The process of claim 3 wherein all monomer is added prior tocommencing the reaction.
 10. The process of claim 3 wherein said monomermixture further comprises up to 15 percent by weight of at least oneother monomer.
 11. The process of claim 3 wherein said monomer mixturefurther comprises up to 10 percent by weight of at least one functionalmonomer.
 12. The process of claim 3 further comprising the addition of aseed polymer to the initial monomer charge.
 13. A process for producinga redispersible polymer powder comprising a) polymerizing a monomermixture comprising vinyl acetate and ethylene in a batch process, in thepresence of a stabilizing system consisting of polyvinyl alcohol, toform an ethylenevinyl acetate polymer dispersion; and b) drying saidpolymer dispersion to form a redispersible polymer powder, wherein saidcopolymer dispersion has a solids level of greater than 65 percent byweight, and a viscosity of less than 5000 mPa.s.
 14. An adhesivecomposition comprising the polymer composition of claim
 1. 15. A coatingcomposition comprising the polymer dispersion of claim
 1. 16. Acementitious composition comprising the polymer composition of claim 1and cement.
 17. A gypsum composition comprising the polymer compositionof claim 1 and gypsum.
 18. A cement and gypsum-free mortar compositioncomprising the polymer of claim 1 and at least one ingredient selectedfrom the group consisting of quartz sand, calcium and magnesiumcarbonates, silicates, cellulose, and calcium oxide.
 19. The use of thecomposition of claim 1 in an adhesive, cementitious formulation, gypsumformulation, cement-free mortar, or gypsum-free mortar.